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Breivik, who is serving a 21-year sentence for killing 77 people last year, has said the attacks were justified because his victims were traitors for embracing multiculturalism.

A court found Breivik sane and said his sentence can be extended for as long as he is considered a danger to society.

In his letter to prison officials, Breivik protested that the censorship of his letters was so strict that his freedom of expression was being impinged upon, Mr Jordet said.

Norwegian tabloid VG, which said it had acquired a copy of the letter, quoted Breivik as saying he was allowed to use only a soft and bendable safety pen described by its manufacturer as "stab-resistant" because it yields at the slightest pressure and cannot be used as a weapon.

Breivik was seen making avid notes with it during his 10-week trial at the Oslo District Court that ended in August.

He has said he wants to write books in prison but that the special pen cramps his hand, describing it as "an almost indescribable manifestation of sadism", VG reported.

Prison officials would not comment on the letter as they were still considering the complaint.

Ellen Bjercke, a spokeswoman for Ila Prison where Breivik is being held, said that Breivik was given an electric typewriter but that it was not connected to his letter of complaint.

It was not clear when Breivik's letter was delivered to prison officials.

During his pre-trial detention, Breivik was allowed a computer that could not be connected to the Internet, but it was taken away from him when he started serving his sentence.

Breivik confessed to setting off a bomb that ripped through Oslo's government district, killing eight people, then opening fire at the summer camp of the governing Labour Party's youth wing on 22 July 2011.